Various methods are known for retarding the surface of mortar or concrete materials to etch the surface, or to expose aggregate at the surface, of such mortar or concrete materials.
In U.S. Pat. No. 7,037,367, Mauchamp et al. disclosed the use of vegetable or mineral oil-based surface retarders for forming wet film coatings on mortar or concrete to provide the retarder active components with a favorable opportunity to penetrate into the surface of the mortar or concrete. Maintaining this penetrating ability facilitated the ability of the surface retarder to etch the treated surface of the mortar or concrete and/or to expose the aggregate on the surface.
In US Publication No. 2003/011998 which issued as U.S. Pat. No. 6,648,963, Pasquier et al. disclosed surface deactivating compositions for concrete or mortar, comprising a retardant, water, and a rheology modifying agent of the HASE type (emulsion, soluble in alkali, of a polymer with hydrophobic modification). A retardant such as carboxylic acid was incorporated into the HASE material at greater than or equal to 0.5% by weight. The process of application consisted in applying this deactivating composition in proportions onto the mortar or concrete surface, then washing the surface after a predetermined period with water. Pasquier et al. also described the use of polydimethylsiloxane, a nonionic surfactant, in their compositions.
A similar approach was disclosed in US Publication No. 20060230987 A1, owned by Sika, wherein Burgals et al. disclosed the use of a similar type of HASE type acrylic resin as a rheology modifying agent in surface-deactivating compositions for concrete or mortar. Their compositions comprised at least one setting retarder and at least one nonionic surfactant, and a process for the application of such a composition. They also taught that their surface deactivating composition could also contain an oil-in-water emulsion, that the use of a cutting oil with the rheology modifying agent made it possible to achieve optimum effectiveness as a curing product, and that the oil could be a “light liquid paraffin.” See Sections 0036-0037.
It is still common practice, particularly in Europe, to wait around for 15-24 hours before washing off the surface of a concrete onto which a set retarder has been applied. The surface retarders, which are of a very high quality, will require a long waiting time before they can be washed off, and the washing will usually take place on the next day. However, the present inventors realized that surface retarding compositions currently in use tend to have poor curing performance and leave cracks in concrete surfaces.
Hence, the present inventors believe that a new composition and method are needed for achieving concrete surface retarders having high curing performance.